some small tweaks.
Replace some uses of 'long' with 'long long' to better support
Win64 builds where 'long' is 32-bit and 'long long' is 64-bit.
On Linux and MacOS, both types are typically 64-bit.
Updated various "MemoryUsage" methods to return 'std::size_t'
instead of 'long' since the latter is 32-bit in Win64 builds.
Updated CHANGELOG.